The Iron Man himself, Robert Downey Jr, admits it's a big call to make from someone with his sized ego.

Despite helming the Marvel monster Iron Man trilogy, Downey jnr expressed admiration for Marvel taking lesser-known names from their deep well of characters and turning Guardians of the Galaxy into one of the biggest hits of the year, with more than $US500 million pulled in at the global box-office to date.

Celebrating the underdogs, he said: "It's like you have a great quarterback, and his brother plays for another team, and then you say: 'Look, this is their second cousin and we think he has a great arm and he should start.' And then he goes and wins the Superbowl."

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Downey jnr is in Toronto for the world premiere of his new drama, legal thriller The Judge, launching at the Toronto International Film Festival.

But he said the success of the other Marvel hits had paved the way to bring its lesser siblings to life in Guardians of the Galaxy.

"We're talking about how the Iron Mans and the Thors and the Captain Americas and the Avengers movies have afforded Marvel the opportunity to essentially take what was a third-tier, minor kind of upstart bit of potential from one of their comic-book series and say: 'Look!'"

Downey jnr is back in the Marvel fold next year in Avengers: Age of Ultron, which will be released in May.

He tweeted a picture featuring the cast and crew having lunch in Richmond England, earlier this year.

Chris Hemsworth, Mark Ruffalo, Chris Evans, Scarlett Johansson and Samuel L. Jackson are all back in costume for the hotly anticipated next instalment, with principal photography finishing up earlier this month.